In recent years, image forming apparatuses based on electrophotographic systems have been introduced in the print-on-demand and shortrun printing markets since such electrophotographic image forming systems make it possible to realize multi item/small-volume printing with small investment, at low running cost, and at low energy consumption. On the other hand, these electrophotographic systems have the problem with their limited options for usable types of paper, compared with offset printing methods, which have heretofore been used. Specifically, the electrophotographic systems are not sufficiently compatible with thick coated printing paper widely employed in catalogue and flier printing, resulting in the present situation which causes the marked decrease in their appeal as commercial products.
Further, the electrophotographic systems cause a problem that transfer media are liable to be bound onto a fixing roller in the process of forming color images with a large toner quantity such as photographic images used in the print-on-demand and shortrun printing markets.
To solve the above problems in the electrophotographic systems, there has been employed a belt fixing system capable of expanding the fixing area (the fixing nip) to transfer more heat energy on fixing, as well as a forced media peeling method as a way to prevent binding to the fixing roller (refer to Patent Document 1). Further, there has been proposed an employment of an electrophotographic toner (hereinafter referred to simply as “toner”), which may be fixed at lower heat energy, incorporating lower melting point resins and lower melting point releasing agents.
However, in the image forming method employing a belt fixing system and a toner, which incorporates the lower melting point resins and the lower melting point releasing agents, it has become clear that the following phenomena are liable to occur in cases of employing relatively thick coated printing paper, and of forming color images with a large quantity of the fixed toner: Blistering image defects caused by space forming between the toner in the fixed image area with a large toner quantity and the transfer medium, and also cyclic non-uniform glossiness caused by temperature decrease of the belt type fixing member.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2005-326668